Crystallization apparatus and method for the formation of crystals in a such apparatus

ABSTRACT

The invention relates to a chamber for the crystallization of solid catalyst carrier. The chamber is provided with an acoustic generator ( 9 ) for loosening the carrier from the walls of the chamber.

FIELD OF THE INVENTION

The invention relates to the preparation of solid catalyst carriers bycrystallization, and concerns crystallization chambers, methods for thecrystallization of the carrier, and methods for removing the carrierfrom the crystallization chamber.

BACKGROUND OF THE INVENTION

Polymerization catalysts, such as Ziegler-Natta type catalysts, areusually deposited on solid carrier particles. The chemical composition,the structure of the surface, the morphology, and the size of theparticles are important for the activity of the catalyst and for theproperties of the polymer to be produced.

Certain carriers, such as MgCl₂*(ROH)_(n), in which R is an alkyl groupand n is 1 to 6, are prepared by melting the substance and thencrystallizing the melt in a spraying chamber. The crystallized particlesare screened in order to remove too small and too big particles. Themelt may be sprayed e.g. through a rotating nozzle, as described in EP655 073. One problem in such processes is that the carrier tends tostick and agglomerate on the walls of the chamber. This decreases theyield and quality of the carrier. Pneumatic hammers have been used forremoving the carrier from the walls. This has, however, not been veryeffective. Hammering also easily damages the chamber.

SUMMARY OF THE INVENTION

Now a chamber for the preparation catalyst carrier by crystallization, amethod for preparing such carrier in a chamber, and a method forremoving such carrier from a chamber have been invented in accordancewith the independent claims. Some preferable embodiments of theinvention are described in the dependent claims.

In accordance with the invention, the chamber is provided with anacoustic generator, which produces a strong sound, which loosens thematerial from the walls of the chamber. The intensity of the sound maybe e.g. 100 to 150 dB, preferably 120 to 140 dB, and most preferably 130to 135 dB. The frequency of the sound is suitably over 5 Hz and below20000 Hz, i.e. broadly at the audible range and below the ultrasonicrange. Most suitably the frequency is below 10000 Hz. Preferably therange is 20 to 5000 Hz, more preferably 100 to 1000 Hz, and mostpreferably 400 to 600 Hz. The duration of the sound signal used may bee.g. 1 to 10 seconds, such as 3 to 7 seconds. The generator ispreferably used at suitable intervals, e.g. at intervals of 0.2 to 2minutes, preferably 0.3 to 0.7 minutes.

The acoustic generator may such as to comprise a vibrating metaldiaphragm, which is vibrated pneumatically. The generator if usuallyprovided with a horn. The horn should be pointed downwards in thechamber.

The chamber is usually a closed vessel surrounded by walls. Thegenerator is preferably mounted in the top wall of the chamber.

The material is preferably removed from the chamber from its bottom. Thechamber is typically an upright cylindrical chamber with a conicalbottom. The volume of an industrial full scale chamber is typically 10to 30 m³, such as 15 to 20 m³.

The carrier may be e.g. a magnesium containing carrier, such asMgCl₂*(ROH)_(n), in which R is an alkyl group and n is 1 to 6. Such acarrier is used especially for Ziegler-Natta type olefin polymerizationcatalysts. Silica is another typical carrier material.

In the crystallization chamber, melted material is sprayed into thechamber where it is cooled and crystallized. Cooling gas may be blowninto the chamber. The cooling gas is preferably an inert gas, such asnitrogen. According to one embodiment, the melt is fed through a nozzleon the top of the chamber. Cooling gas is also fed on the top of thechamber. Additional cooling gas may be fed on a lower position. Thesecond cooling gas usually has lower temperature.

In accordance with the invention, sticking of the catalyst material onthe walls and outlet of the chamber and agglomeration of the catalystmaterial particles is effectively prevented. This is especiallyadvantageous when the material is removed continuously from the chamber.The fraction of too large particles to be rejected is also thusdecreased. The quality of the material is not decreased. No damage iscaused to the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The enclosed drawings form a part of the written description of theinvention.

FIG. 1 shows the preparation of a catalyst carrier by a sprayingprocess.

DETAILED DISCLOSURE OF SOME EMBODIMENTS OF THE INVENTION

FIG. 1 describes the preparation of a MgCl₂*(C₂H₅OH)_(n) carriermaterial. The material is melted and fed through line 1 and nozzle 2 onthe top of spraying chamber 3. The flow rate of the melt is F1 andtemperature T1. Nitrogen is fed through line 4 on the top of thechamber. The flow rate is F2 and the temperature T2. T2 is lower thanT1. A second nitrogen flow is fed through line 5 into the lower part ofthe chamber just above the conical bottom. The flow rate is F3 and thetemperature T3. T3 is lower than T2. The carrier material crystallizesin the chamber and falls at the bottom, from where it is continuouslyremoved through line 6 to screen 7. Gases are removed from the chamberthrough line 8.

An acoustic generator 9 (Nirafon, Lahti, Finland) is mounted inside thechamber 3 at the top, the horn pointing downwards into the chamber. Thegenerator comprises a vibrating diaphragm at the frequency of 500 Hz.The maximum intensity of the sound is 135 dB. The horn is operated with7 to 8 bar nitrogen.

The process was run under the following conditions: F1 T1 F2 T2 F3 T3kg/h ° C. kg/h ° C. kg/h ° C. 25 115 340 64 650 −21

The acoustic generator 9 was blown for 5 sec after each 30 sec.

The process could be run without the material blocking the bottom outletor sheeting the chamber walls. The longest uninterrupted run was 15days. Even after that no sign of the carrier depositing on the walls oroutlet was found.

As a comparison, the acoustic generator 9 was switched off. An immediatesmall drop in the outlet rate was observed. After 6 hours the outlet wastotally blocked and it had to be opened. The run was continued and after3 hours the outlet was almost totally blocked again. When the acousticgenerator was taken in use again, after 15 hours a sudden flood ofmaterial was observed. This material had obviously been deposited on thewalls of the chamber and was now suddenly dropped.

1. Chamber for the crystallization of solid catalyst carrier,characterized in that the chamber is provided with an acoustic generator(9) generating a sound with the intensity of at least 100 dB forloosening the carrier from the walls of the chamber.
 2. Chamberaccording to claim 1, wherein the chamber comprises a top wall and theacoustic generator (9) is mounted in the top wall.
 3. Method for thepreparation of solid catalyst carrier, in which method the carrier isformed in a chamber, characterized in that the inside of the chamber issubjected to a sound, the intensity of which is at least 100 dB,generated by an acoustic generator (9) for loosening the carrier fromthe walls of the chamber.
 4. Method according to claim 3, wherein theintensity of the sound is at least 120 dB, and preferably at least 130dB.
 5. Method according to claim 3, wherein the frequency of the soundis over 5 Hz and below 20000 Hz, suitably below 10000 Hz, preferably 20to 5000 Hz, more preferably 100 to 1000 Hz, and most preferably 400 to600 Hz.
 6. Method according to claim 3, wherein the duration of thesound is 1 to 10 seconds, preferably 3 to 7 seconds.
 7. Method accordingto claim 3, wherein the sound is generated periodically, such as atintervals of 0.2 to 2 minutes, preferably at intervals 0.3 to 0.7minutes.
 8. Method for removing crystallized solid catalyst carrier fromthe walls of a chamber, characterized in that the inside of the chamberis subjected to a sound, the intensity of which is at least 100 dB,generated by an acoustic generator (9) for loosening the carrier fromthe chamber.
 9. Method according to claim 8, wherein the carrier isremoved continuously from the chamber.
 10. Use of an acoustic generator(9) generating a sound with the intensity of at least 100 dB forloosening crystallized solid catalyst carrier from the walls of achamber.
 11. Method according to claim 4, wherein the frequency of thesound is over 5 Hz and below 20000 Hz, suitably below 10000 Hz,preferably 20 to 5000 Hz, more preferably 100 to 1000 Hz, and mostpreferably 400 to 600 Hz.